This invention is generally related to methods and compositions for treating subterranean formations, and more particularly to treatment fluids having additives that modify the fluid's rheological characteristics.
Polymeric agents, such as cationic polymers, high molecular weight polyacrylamide polymers, polysaccharides, synthetic polymers, and the like, have previously been added to treatment fluids to obtain the desired properties for a variety of subterranean treatments. Such treatments include, but are not limited to, drilling, stimulation treatments (e.g., fracturing treatments, acidizing treatments, etc.), and completion operations (e.g., cementing, sand control treatments like gravel packing, etc.). As used herein, the term “treatment,” or “treating,” refers to any subterranean operation that uses a fluid in conjunction with a desired function and/or for a desired purpose. The term “treatment,” or “treating,” does not imply any particular action by the fluid or any particular component thereof.
Traditional treatment fluids may be grouped into two classifications. Such classifications include oil-based treatment fluids and aqueous-based treatment fluids. While oil-based treatment fluids can have superior performance characteristics, aqueous-based treatment fluids may be more economical to use and less damaging to the formation and to the environment.
It is often important to consider a fluid's rheological parameters when assessing the utility of a treatment fluid for a given purpose. For use as a subterranean treatment fluid, a fluid generally should be capable of maintaining a viscosity suitable for the desired operation. For example, a drilling fluid preferably has a sufficient viscosity to be capable of transporting the drill cuttings to the surface without being so viscous as to interfere with the drilling operation. Similarly, a cementing fluid preferably has a viscosity sufficient to prevent separation of solid cement components from the liquid components for a sufficient time to allow the cement to set. However, increased fluid viscosity (e.g., cement viscosity, drilling fluid viscosity, etc.) can result in problematic sticking of the drill string and increased circulating pressures that may contribute to lost circulation problems in the formation. Solid particles such as various clays are commonly used as a way to maintain sufficient viscosity in such treatment fluids. These solid particles may require vigorous agitation in the fluid to reach a fully active state and provide an increase in viscosity. Time pressures may demand that fluids be prepared quickly for shipment to the drilling operation. As a result, inadequate shear and over-treatment may occur when using solid particles. Additionally, solid particles may affect both the viscosity of the fluid and the fluid's yield point, which is a measure of the initial force required to cause the fluid to flow.
In addition to prevent separation of solid cement components from the liquid components under both dynamic and static conditions, the cementing fluids should possess a low enough viscosity while under shear (during pumping) so that efficient placement of such fluids even in the narrower annulus could be achieved, cases may be anticipated due to highly eccentric casing placement.
Aqueous treatment fluids which do not contain solid particles may offer many advantages if they can retains the performance of an oil-based treatment fluid while maintaining the many of the benefits of using an aqueous-based treatment fluid.